The double-lined section of U.S. 91-466 in the above map shows the location of the new section of Interstate freeway.
From California Highways and Public Works magazine, September-October 1961 issue.
By L. M. Barnett, District Construction Engineer
A $5,000,000, 25 mile section of Interstate 15, carrying U.S. 91 and U.S. 466 on the stretch between Barstow and Las Vegas is now completed. Work was started by Contractors Gordon H. Ball, Ball & Simpson, and E. L. Yeager in April, 1960, and the first 14 miles were opened to traffic on July 19, 1961. The entire project was completed in September.
Beginning 1 1/2 miles east of Baker (the junction with Route 127 to Death Valley), the portion already completed has long been referred to as the "Bloody Baker Grade." This name resulted from a number of spectacular traffic accidents, mainly of the head-on collision type, which have taken place due to excessive speed on the long westbound downgrade, sometimes at speeds over 100 MPH. While a new highway cannot be expected to put the damper on such drivers, it is expected that the new four-lane divided construction, with a 100-foot median area, will provide more protection for other motorists who sometimes become innocent victims of an "out of control" vehicle.
Accident Rate Normal
In recent years, due to aerial patrols and other special enforcement by the California Highway Patrol, the over all accident and fatality rate on the Baker Grade has not been greater than normal for a rural State highway carrying in the neighborhood of 5,000 vehicles per day. Weekend peak traffic volumes, which are swelled by the Los Angeles to Las Vegas recreational trips, frequently reach over 500 vehicles per hour in one direction. For these reasons, this project near the middle of the Interstate route between Barstow and the Nevada State Line (a distance of 111 miles) was selected for first construction.
One special feature of this project was the care taken to avoid disturbance of the native desert vegetation, in order to provide erosion protection and to act as a screen between the two opposing streams of traffic. Hauling on or crossing of the median was restricted during construction, except at designated places where it was necessary to obtain access for construction of bridges or drainage structures.
Beginning in the early design stages, the makeup of the structural section of the road, including pavement and base materials, has been of considerable interest. The sections finally adopted are shown in the accompanying sketches. One section is being used for the new roadbed and the other as an overlay of the existing roadbed. The new roadbed utilizes a 7 inch asphalt concrete pavement (an experimental section) on an 8 inch aggregate base. Additional subbase (up to 6 inches) was called for over portions where poor basement soil was encountered.
Existing Road Resurfaced
The existing road was resurfaced to serve as the eastbound freeway roadbed through most of the project. The new pavement consists of three courses of asphalt concrete topped by 1/2 inch of open-graded asphalt concrete. Efforts by the Contractor and inspectors resulted in an unusually smooth riding surface on the resurfaced roadbed. Leveling courses were placed by means of motor graders with highly skilled operators. The old pavement had irregular profile and variable transverse slope. Both of these deficiencies were corrected by use of a planned grade line and single cross slope put into the first leveling course. The profilograph reading on the first averaged 0.14 inch per mile.
Contrary to what might have been expected, high quality alluvial gravel was not easily found in the vicinity of this project. Assorted soft, mineral bearing rocks, frequently coated with an undesirable carbonate, were more typical. The carbonate apparently results from drying out of hot weather rainfall after seeping below the surface. It is found in thin layers pocketed throughout depths of more than 20 feet in the alluvial deposits. It was rejected for use in the upper layers of the roadbed. Extensive preliminary studies for possible aggregate sources included 11 test pits, which were left open for viewing by prospective bidders on the construction work. Borrow material was obtained from 7 sites near to the road, selected for suitability of material and economy of haul. Hauling was by means of tractor scraper units; average haul being about three miles, with some hauls of base material over six miles.
Water is scarce
Water, a scarce item on thc desert, required for compaction of earthwork and base material, was supplied from two reservoirs, one at Halloran Summit and one at the northeast end of the project. Wells near Cima Road supplied the reservoirs. From the reservoirs, water was piped by gravity and booster pumps to six 10,000-gallon tanks, which were strung along the job at about one-mile intervals. Tanks were moved ahead as the work progressed toward the south. About 20 miles of six-inch steel water main were used, with deliveries of over 300,000 gallons per day at times.
Grading work consisted of shallow cuts and fills for the most part, but the Halloran Summit is crossed by a cut about one mile long and of 40 feet maximum depth.
Ten bridges were included in the project, with spans of 100 to 200 feet. All were of precast deck and substructure units, hauled to the project from a casting yard at Barstow. There were also three welded steel plate girder structures, providing crossings over the freeway at Halloran Springs, Halloran Summit, and Cima Road. Although the project reaches elevations over 4100 feet at the summit, a relatively mild winter and careful scheduling by the Contractor permitted almost continuous work.. Summer thunderstorms and attendant localized flash floods posed some problems during the course of the job.
First Rest Areas
This proect contains the first "safety rest areas" built as part of the road contract on an interstate job in District VIII as may be seen by photographs accompanying this article, The "safety rest areas" are within the right of way and have freeway-type exits and entrances. Parking areas, water supply and landscaping were provided under the contract. The remote location of this project made it necessary to establish living quarters for both Contractor and State personnel. Facilities in Baker were soon overtaxed by the influx of construction workers, many of whom brought house trailers and families with them. At the time of peak construction work, eighteen State inspectors were living in quarters provided through temporary use of service station and motel buildings at Yucca Grove, near Halloran Summit.
These buildings were within the freeway right of way and were removed during later stages of the work.
Resident Engineers on the job were C. M. Mauck and J. O. Erwin.
